1. Field of the Invention
The present invention relates to a method of distributing and transporting powdered or granular material such as pulverized coal, refining agent or the like from a pressurizing tank for transportation to a plurality of feeding ends such as tuyeres of a blast furnace. More particularly, the invention is concerned with a method of distributing and transporting powdered particles or granular material in which the material is distributed and transported from a single transportation pressurizing tank to a plurality of feeding ends through respective transportation pipes connected to the pressurizing tank at discharging rates which are determined beforehand for respective transportation pipes, without necessitating any specific distributing device.
2. Prior Art
A typical known system for continuously supplying a material to a plurality of feeding ends is shown in, for example, Japanese Patent Publication No. 29684/1976 corresponding to U.S. Pat. No. 3,720,351 and German Pat. No. 2,243,439. In this known system, two or more batch tanks arranged in parallel are used alternatingly or one after another to deliver the material to the tuyeres through a specific distributor. This known system, however, employs a large amount of equipment which in turn occupies an impractically large installation area and necessitates a complicated piping arrangement. In addition, there is a fatal disadvantage of being unable to control the discharging rates of material through respective transportation pipes independently.
U.S. Pat. No. 3,230,016 discloses, by way of example, a series type distributing and transporting apparatus having a lower chamber which accomodates a distributor constituted of an inversed-conical hopper consisting of a pair of cones to which transportation pipes are connected independently. In this apparatus, therefore, the construction of the tank is impractically complicated. In addition, since the material is moved downwardly in the tank, it is necessary that discharge nozzles have a comparatively small diameter, in order to prevent intermittent floodability which is often experienced when the handled material has a strong adhesion as generally shown by material having small particle sizes. The reduced diameter of the nozzle inevitably increases the tendency of plugging in the nozzle. Thus, the prevention of floodability and prevention of plugging of the nozzle are generally incompatible with each other. This apparatus, therefore, cannot be used suitably for the transportation of powdered or granular materials exhibiting inferior transportation characteristics and cannot apply to a large variety of physical properties of the powdered or granular material.
Under this circumstance, the present applicant has filed a Patent application on an invention entitled "Method of and Apparatus for Distributing Powdered Particles" (filed May 3, 1982, Ser. No. 374,313). The invention of this application employs a pressurizing tank provided with a weighing device, and a plurality of transportation pipes which open at their one ends to the fluidized bed in the tank and connected at their other ends to different feeding ends. In operation, the powdered granular material is directly distributed and transported from the pressurizing tank to the feeding ends through the transportation pipes. During the transporting operation, the velocity of a gas through the fluidized bed is controlled and maintained substantially at a constant valve by a pressure regulating signal determined by a first factor which is a rate of change in the weight of the tank including the weight of the material contained by the tank and a secondary factor which is the internal pressure of the tank, and the flow rates of booster gas supplied to respective transportation pipes are controlled independently to attain desired flow rates of the powdered or granular material in the transportation pipes. The control of the flow rate of the booster gas in each transportation pipe is made by means of a differential pressure signal corresponding to the differential pressure across the discharge nozzle of each transportation pipe. The distribution and transportation apparatus of the type described permits distribution and transportation of the powdered or granular material to the feeding ends at desired flow rates very well. In order to achieve higher accuracy in the distribution and transportation of the powdered or granular material, however, it is necessary to employ a more practical way of control. For instance, although the control of the flow rate of the booster gas in each transportation pipe is achieved in accordance with the differential pressure across the discharge nozzle, it is necessary to take into account the difference between the mass flow rate of the powdered or granular material in each transportation pipe attained through the above-mentioned control and the actual mass flow rate of the powdered or granular material in each transportation pipe, in order to achieve higher accuracy of the distribution and transportation.